Projection screen of retractable type

ABSTRACT

A retractable projection screen that is transparent to sound waves and that includes at least two layers of white fabric that are superimposed and joined together. The screen including the two layers of superimposed fabric is rolled onto a rolling-up device, the weighting bar of which is of a sufficient weight for stretching the fabric so that the stretching compensates for the difference in diameter between the two layers when they are rolled up, which makes it possible to avoid the formation of a fold in the inner layer of fabric when the screen is rolled up.

[0001] The present invention relates to a projection screen ofretractable type, adapted to be used in an extended position incombination with a projector, in particular a video projector, and witha sound broadcasting device.

[0002] More precisely, a screen according to the present invention isretracted when not in use, in order both to make it less cumbersome andto avoid the risk of its becoming dirtied and/or deteriorated.

[0003] Furthermore, a screen according to the present invention is ofthe type known as acoustically transparent, which is to say that it ispermeable to sound waves.

[0004] This makes it possible to implement simultaneously the projectionof video together with sound broadcasting coming from sound sourcesplaced behind the acoustically transparent screen.

[0005] The advantage of placing the sound sources behind the screen hasbeen known since the existence of film with sound, known as “talkingpictures”. This is to procure the sensation of coherence between theprojected image and the sound diffused for the spectator.

[0006] The simultaneous implementation of sound sources and anacoustically transparent video screen makes it possible to reproducethis sensation in a smaller environment, in particular a domesticenvironment.

[0007] Video screens combining the features mentioned above are known.

[0008] Conventionally, such screens are formed from a sheet of plasticsmaterial, generally PVC, perforated with orifices of small size adaptedto let through sound waves.

[0009] Such screens are formed from a sheet of PVC of which theperforations typically represent between 2% and 6% of their surface andlet the sound through only very imperfectly. A large part of the soundis reflected, instead of passing though the orifices that perforate thescreen. This phenomenon causes substantial attenuation of the soundlevel, particularly at high frequencies. Furthermore, the multiplereflections created initially by the full portions of the screen causeaberrations in the acoustic response, resulting in irregularities in thetransfer function and in distortions that degrade the sound quality.

[0010] In addition, in an environment that is more restricted than aconventional movie theater, the spectator is normally placed much closerto the screen. The perforations of the screen, closer than a certaindistance, become visible, and add a raster effect to the image which isbothersome.

[0011] Such screens are in general retractable through rolling onto acylinder rotated by a motor, and frequent repetition of this operationgives rise to deformation either on the edges of the screen, or on themedian part. This arises from the fact that screens that can be rolledup are not generally tensioned by the edges, but only by a weightingbar, which applies a vertical stretching force to the screen, towardsthe bottom.

[0012] With time, the material making up the screen can stretch in anuneven manner, thereby giving rise to deformations that risk impairingthe flatness of the screen. Apart from the esthetic drawbacks that thisimplies, the focusing of the projector is put out, so altering thequality of the image in certain zones.

[0013] This defect is made all the worse if acoustically transparentscreens having perforations are used.

[0014] Many devices exist for tensioning the edges of screens that rollup, but they are generally both costly and unaesthetic, and can also jamdue to wear.

[0015] The object of the present invention is to provide an acousticallytransparent retractable screen without the drawbacks mentioned above.

[0016] More precisely, the present invention relates to a projectionscreen that is transparent to sound waves, of the retractable kind,characterized in that it comprises at least two layers of white fabricsuperimposed and joined together.

[0017] According to a first embodiment of the invention, the screencomprising two layers of superimposed fabric is rolled onto rolling-upmeans, the said weighting bar being of sufficient weight for stretchingthe fabric so that the stretching compensates for the difference indiameter between the two layers when they are rolled up.

[0018] This makes it possible to avoid the formation of a fold in theinner layer of fabric, when the screen is rolled up.

[0019] According to a second embodiment of the invention, the screenfolds into a plurality of rectangles linked by folds when the weightingbar rises under the effect of the traction means that are applied to it.

[0020] According to a third embodiment of the invention, a piece offabric forming the screen is fixed by one edge defining a first end, anopposite end being fixed to a rolling-up means comprising a rollerdisposed in a fixed manner parallel to the said first end, a mobileroller serving as a weighting bar being interposed between the two endsso as to tension the fabric towards the bottom by gravity, said rollerbeing fixed to pressing means tending to make contact between two layersof fabric which are thus disposed back to back.

[0021] Preferably the rolling-up means comprises means enabling thesimultaneous retraction of a sound broadcasting device in such a mannerthat the said device is situated substantially at mid-height behind thescreen when the latter is in the extended position.

[0022] The features and advantages of the present invention will bebetter understood on reading the following detailed description, withreference to the accompanying drawings in which:

[0023]FIG. 1 is a front elevation view in the unrolled position of aconventional screen that can be rolled up,

[0024]FIG. 2 is a cross-section view in the unrolled position of aconventional screen that can be rolled up,

[0025]FIG. 3 is a front elevation view of a first embodiment of theinvention, the screen being in the unrolled position,

[0026]FIG. 4 is a cross-section view of a first embodiment of theinvention, the screen being in the unrolled position,

[0027]FIG. 5 is a cross-section view of a screen according to a secondembodiment of the invention, the screen being in the unrolled position,

[0028]FIG. 6 is a front elevation view of a screen according to a secondembodiment of the invention,

[0029]FIG. 7 shows in detail a side edge of a screen according to asecond embodiment of the invention,

[0030]FIG. 8 is a diagrammatic view in cross-section of a thirdembodiment of the invention, the screen being in a partially retractedposition.

[0031]FIG. 9 is a detailed cross-section view of a third embodiment ofthe invention, and.

[0032]FIG. 10 is a diagrammatic side elevation view of an embodiment ofthe invention associated with a retractable sound broadcasting device.

[0033] Considering in more detail, a conventional retractable screen ofthe type that can be rolled up, such as shown in FIGS. 1 and 2,comprises a band of material 10 of white color of substantially uniformwidth, rolled onto a roller 11 of which the rotation is controlled by amotor 12 that rotates axially. The band 10 comprises a free end 13 whichis folded and fixed so as to form a hem in which is disposed a weightingbar 14. A split tube 15 is disposed around the weighted hem. Twodemountable stoppers 16, 16′ are generally provided to close the splittube 15 in order to avoid any axial displacement of the weighting bar inthe hem.

[0034] The motor 12 is generally of the type with adjustable end oftravel, a reversing device being provided for changing its direction ofrotation. When the motor is activated, it rotates the roller 11 whichrolls up or unrolls the band 10 according to the direction of rotation.

[0035] When the band is unrolled, the motor 12 stops at the end oftravel in a position predetermined by the adjustment. It is tensioned bythe force of gravity which acts on the weighting bar 14. When the motoris started again, the reversing device reverses the direction ofrotation of the motor, which rolls up the band 10 around the roller 11until activation of the end of travel device, which is adjusted so as tointerrupt the action of the motor when the band is sufficiently rolledup onto the roller 11.

[0036] The band 10 is generally constituted by an opaque, whitematerial, which reflects light, which makes possible its use for aprojection screen for cinematographic, photographic, computer or videoapplications.

[0037] In applications requiring sound broadcasting that is simultaneouswith the image, it is generally preferred to have a source of sound (notshown) behind the screen. The sound waves emitted by the source ofsound, generally a loud-speaker, pass through the band 10, which isgenerally constituted by a sheet of plastics material, and which isperforated by a multitude of orifices provided for this purpose.

[0038] Such orifices are generally of a diameter in the range between0.5 and 1.5 mm. Their total surface typically represents between 2% and6% of the total surface of the screen.

[0039] This proportion of perforated surface is insufficient to permitthe correct transmission of sound, a proportion of at least 40% beingnecessary.

[0040] A surface perforated to the extent of 40% or more of the surfaceof the screen is incompatible with an acceptable performance incinematographic or video projection.

[0041] Apart from this, fabrics are known in the production ofprojection screens. These have the advantage, in certain textures, ofbeing permeable to sound waves.

[0042] The disadvantage of fabrics that are sufficiently permeable tosound waves is their lack of opacity to light, which gives rise to aloss in the brightness of the projected images. Moreover, the lack ofopacity of such fabrics can give rise to the appearance of a perceptiblereflection on the screen, interfering with the projected image, when asurface situated behind the screen reflects the light.

[0043] If the improving the opacity of a screen made of sound-permeablefabric can be envisaged by using a tighter weave, and thereby increasingits density, its permeability to sound is correspondingly reduced.

[0044] The inventor observed that, in a surprising manner, it waspossible to reconcile the need for sufficient sound permeability withsufficient opacity to light by substituting a fabric of density x,insufficiently permeable to sound, by two layers joined together ofdensity x/2 of the same fabric of which the overall permeability tosound waves turns out to be well above that of the fabric of density x.

[0045] A projection screen according to the invention, such as shown inFIGS. 3 to 10, is free from the drawbacks and limitations mentionedabove concerning conventional acoustically transparent screens that canbe rolled up.

[0046] According to a first embodiment of the invention, such as shownin FIGS. 3 and 4, a projection screen 17 comprises two thicknesses of anexpanse of white fabric, permeable to the air. Preferably, and in anon-limiting manner, fabric is used comprising 30 to 80 threads of warp,and 20 to 40 picks of weft, per square centimeter.

[0047] Preferably, and in a non-limiting manner, the mass of fabric perunit area is between 150 and 200 grams per square meter. These twothicknesses, of the same dimensions and of rectangular form, can be sowntogether.

[0048] It is also possible to fold the fabric back on itself to form twothicknesses, and to sow the side edges together, as well as the two endsof the expanse of fabric.

[0049] The assembly constitutes the screen and comprises two visiblelateral seams 18, 19, an end 20 known as the roll-up end, the oppositeend 21 (FIG. 4) being known as the weighting end.

[0050] End 21 comprises, in a non-limiting manner, a hem open at bothends, formed in conventional manner by means of a seam 22.

[0051] A weighting bar 23, comprising, for example, a bar of solidsteel, is disposed inside the hem of the end 21. Preferably, the lengthof the weighting bar 23 is closely similar to that of the width ofscreen 17, in order for the mechanical tension due to the mass of thebar to be evenly distributed over the whole width of the screen.

[0052] The mass of the weighting bar 23 will be proportional to thesurface area of the screen, and preferably at least equal to 3 kilogramsper square meter of screen surface area.

[0053] The maximum mass of the bar will be determined so as to avoidtearing of the fabric around the seam 22.

[0054] The assembly comprising the end 21 of the screen and theweighting bar 23 disposed inside the hem is itself disposed inside arigid tube 24 that is split over the whole of its length.

[0055] Its length is at least equal to the width of the screen 17. Thescreen 17 is disposed so as to pass through the split in the tube 24.Two stoppers 25 block respectively the ends of the tube, to avoid axialdisplacement of the weighting bar and/or hem 21 in the tube 24.

[0056] The roll-up end 20 of the screen 17 is fixed by suitable means tothe rolling-up means comprising for example a roller 27 that isrotationally fixed to the outer face of a driving motor 28 of generallycylindrical form (represented symbolically by a cross, FIG. 4) axiallydisposed inside the roller 27. The motor 28 comprises an axle fixed to afixed support 29 (FIG. 3).

[0057] The motor 28 is adapted to rotate the roller 27 in one directionor the other, according to the status of a control device (not shown).An end of travel device is provided so as to interrupt the operation ofthe motor as soon as a set number of rotations has been achieved.

[0058] The end of travel device comprises a reversing device adapted toreverse the status of the motor control simultaneously with theinterruption of its operation.

[0059] The roller 27 comprises an axle 30 which is rotationally coupledto it, and of which an end projecting axially from the roller 27 issupported by a fixed support 29′ comprising, for example, a bearing.

[0060] Such drive means are known per se, particularly in devices forautomatically raising blinds, and do not constitute a feature of theinvention.

[0061] When the control device is operated, the motor 28 rotates theroller 27, which rolls up the screen 17 onto the roller.

[0062] The weighting bar 23 simultaneously tensions the two layers ofthe screen 27. The rolling up of the screen onto the roller defines aninner layer and an outer layer of which the radius exceeds that of theinner layer by one thickness of fabric.

[0063] For each turn rolled up, the difference in length between the twolayers is thus

2πe,

[0064] e being the thickness of the fabric.

[0065] The weighting bar 23 exerts, by its mass, sufficient tension tostretch the outer layer such that its elastic deformation is at leastequal to the difference in length between the two layers.

[0066] This avoids the formation of folds to take up the difference inlength between the two layers, which causes visible marks on the screenand premature wear around these folds.

[0067] Moreover, by virtue of the elasticity of the fabric, the tensionexerted by the weighting bar 23 takes up the possible non-elasticdeformations that may arise in the different parts of the screen 17, andprocures sufficient flatness for the screen in the unrolled position toallow satisfactory image projection.

[0068] A second embodiment of the invention is shown in FIGS. 5 to 7. Ascreen 31 comprising two layers of fabric fixed by an edge termed theupper edge, using means that are known per se, to an upper fixing bar 32that is fixed to a frame (not shown).

[0069] The screen 31 is also fixed by its opposite edge, termed thelower edge, to a weighting bar 33.

[0070] The two edges 34 and 34′ of the screen 31, termed lateral edges,each comprise a sown hem 35 and 35′ respectively.

[0071] Inside each of these hems a plurality of elements 36 are providedthat are flat, rigid and oblong (FIG. 7) and disposed in line but notjoined together.

[0072] All the elements 36 are identical, and four elements 37,identical to each other and of length substantially equal to half thatof an element 36, are disposed respectively at each end of the two linesof elements 36.

[0073] The elements 36 and 37 are disposed inside the hems and arespaced at equal intervals.

[0074] It is possible, in a variant form, to connect the elements 36 and37 together by a flexible or semi-rigid band (not shown) of widthsubstantially equal to that of the elements 36 and 37.

[0075] The elements 36 are perforated in their center by an oblong hole38, of which the axis is perpendicular to that of the element 36.

[0076] The hems comprise several oblong openings 39, sown or riveted,which are each placed over, and correspond with, one of the respectiveholes 38 provided in the elements 36.

[0077] Two straps 40 are provided, passing into each of the hems bymeans of the holes 38 and openings 39 alternately in front of and behindthe screen 30.

[0078] An end termed the lower end of each strap 40 is connected to theweighting bar 33, the other end termed the upper end being fixed so asto be able to be rolled up by the rolling-up means.

[0079] Two recesses (not shown) are provided in the upper fixing bar 32to permit movement of each strap 40 without friction when it is rolledup by the rolling-up means.

[0080] The rolling-up means comprise, in a manner similar to theprevious embodiment, a roller 42 rotationally coupled to a motor 43(shown symbolically in FIG. 5), said motor 43 being of the type withcontrol reversal at the end of travel, as in the previous embodiment.

[0081] The roller 42 is provided with two pairs of circular guideflanges 44 disposed coaxially of the roller, each flange of a pair beingspaced from the other by a distance equal to or greater than the widthof the strap 40 plus a clearance.

[0082] The separation between the two pairs of flanges is equal to theseparation between the two straps when disposed in their holes 38 andopenings 39.

[0083] The assembly comprising the straps 40, the rolling-up means 41and the guide flanges 44 constitutes the driving means adapted toactuate the folding up of the screen.

[0084] When the motor 43 rotates the roller 42, the two straps 40 rollup around the roller 42, while being guided by the guide flanges 44.This action pulls up the weighting bar 33 which folds up the screen 31into a succession of rectangular parts 45 defined by the length of theelements 36 and 37 and by the width of the screen 31. These rectangularparts are connected by folds 46 which form in the gaps separating theelements 36 from each other and also in the gaps separating the elements36 and 37.

[0085] These folds 46 are represented by gray bands in FIG. 6.

[0086] The screen is thus forced to fold up in a zigzag, in the mannerof a road map.

[0087] The end of travel device of the motor 43 is adjusted such that,when the weighting bar 33 is at a distance from the upper fixing bar 32substantially equal to the product of the thickness of a seam of thescreen 30 containing an element 36 or 37 multiplied by the number ofelements 36, 37 disposed in a seam of the screen, the said end of traveldevice interrupts the operation of the motor 43 and operates a reversingdevice which reverses the direction of rotation of the motor the nexttime it is started.

[0088] Thus, when the motor starts to turn once again due to the actionof a control, it unwinds the straps 40. The weighting bar 33 pullsdownwardly both the straps 40 and the screen 31 by gravity. The screen31 unfolds until it is completely tensioned by the weighting bar 33.

[0089] The end of travel device of the motor 43 is adjusted so as tointerrupt the operation of the motor when the straps 40 are sufficientlyunwound to no longer be tensioned by the weighting bar, the weightingbar being supported solely by the screen 30.

[0090] The end of travel device operates a reversing device, as before.Thus, the next time the motor 43 is started, the direction of rotationof the motor will cause the straps 40 to be wound up.

[0091] A variant of the first two embodiments of the invention providesa fixed support 45 (FIG. 8) extending substantially horizontally behindthe screen 31, and a roller 46 disposed parallel to the roller 42supported, for example, by bearings. A black opaque band 47, for exampleof fabric, and of width substantially equal to the separation betweenthe pairs of flanges 44, is fixed to the roller 42 by one of its ends.The opposite end is provided with a weighting bar. In this case therolling-up means are disposed in front of the screen 31.

[0092] When the straps 40 unwind, the band 47 also unrolls untilinterruption of the action of the motor. The light projected onto thescreen 31 from the front is principally reflected, as intended. Part ofthe light, nevertheless, passes through the screen 31. This light isthen absorbed by the band 47, by virtue of its black color.

[0093] This avoids the light reflecting on some other surface seorificevant behind the screen 31 coming, by transparency, to interferewith the image projected onto the screen 31.

[0094] Advantageously, when the sources of sound 48 are placed behindthe screen 31, the support 45 extends sufficiently behind the screen 31for the roller 46 to be disposed behind the said sources of sound. Thus,when it descends simultaneously with the extension of the screen 31, theband 47 extends vertically behind the sources of sound 48.

[0095] When the sources of sound 48 are fixed in such a manner as tomake it impossible to pass the band 47 behind the sources of sound 48,provision is made to make it from acoustically transparent material.

[0096] Another embodiment comprises rolling-up means 50 (FIG. 9),similar to those already described.

[0097] A band of acoustically transparent fabric 51 adapted to reflectlight is fixed by one end to rolling-up means 50 comprising, in aconventional manner, a drive roller rotationally coupled to a motorprovided with an end of travel device.

[0098] Three rollers termed lower rollers 54, 55, 56 (FIGS. 9 and 10)are parallel to the rolling-up means 50 and are fixed by their ends to asupport 57, their axes substantially forming an isosceles triangle withthe vertex at the bottom. A first roller 54 is fixed, and a secondroller 55 of which the axis defines the vertex of the said triangle isalso fixed. Advantageously, the second roller is of greater diameterthan the first roller.

[0099] A third roller 56, substantially of the same diameter as the saidfirst roller 54, is connected to the supports 57 in order for its axisto be able to move in a path limited by the said support.

[0100] Elastic means (not shown) are provided, tending to move the saidmobile third roller 56 towards the said first roller 54. The action ofsaid elastic means is represented by an arrow shown in FIG. 10.

[0101] The rollers 54 and 56, in combination with the elastic means,constitute a means for pressing together the two layers of the band offabric 51, 51′, coupled in their movement to the roller 55.

[0102] The part 51′ of the band of fabric indicates that which rises upto the rolling-up means 50. It is fixed at its end by a seam 52,parallel to the drive means 50.

[0103] In order to visualize the two layers 51 and 51′ of the band offabric, they are represented separately in FIGS. 9 and 10, but it shouldbe understood that they are in fact joined together.

[0104] The rollers 54 and 56 can, in a variant form of the invention, bereplaced by any means of parallel guidance, for example permitting theband of fabric to slip.

[0105] The combination of such guide means with elastic means movingthem towards each other defines the said means for pressing together thetwo layers of the band of fabric 51, 51′.

[0106] The band of fabric 51, 51′ is disposed so as to pass between thefirst and third lower rollers 54, 56, to pass around the second lowerroller 55, to pass a second time between the first and third lowerrollers 54, 56, and to be fixed at its end by the seam 52 to its otherpart 51, itself fixed to the rolling-up means 50.

[0107] The assembly 58 constituted by the three lower rollers (54, 55,56) and by their supports 57 is mobile and of sufficient mass to tensionthe band of fabric 51 by gravity.

[0108] When the rolling-up means rolls up the band of fabric 51, 51′,the part which is not rolled up reduces, pulling the assembly 58upwardly. The end of travel device provided in the rolling-up means 50is adjusted so as to interrupt the action of the rolling-up means and toreverse it at the next control operation when the assembly 58 arrives ata predetermined position, near to the rolling-up means 50.

[0109] When the rolling-up means unroll the band of fabric 51, 51′ thisis drawn downwardly and tensioned by the mass of the mobile assembly 58.

[0110] The rollers 54 and 56 press the two thicknesses 51 and 51′ of theband against each other so as to form an acoustically transparentprojection screen comprising two layers of white fabric.

[0111] A further variant of the embodiments of the invention comprises afixed support 45 (FIG. 10) extending substantially horizontally behindthe screen 30, and a roller 46 disposed parallel to the roller 42supported, for example, by bearings. A drive means for rotating theroller 46 comprises for example a transmission belt 47 whichrotationally couples the roller 42 with the roller 46.

[0112] Advantageously, in this case, the diameter of the roller 46 ishalf that of the roller 42.

[0113] Any other means of driving the roller 46 can be envisaged, ofwhich the action is synchronized with the rotation of the roller 42.

[0114] A pair of straps 48 is fixed by one end to the roller 46, theother end being fixed by fixing means 49 to a sound broadcasting device60 comprising at least one loudspeaker 61.

[0115] Preferably the sound broadcasting device 60 comprises threeindependent acoustic units brought together so as to form a mechanicallyconnected assembly which is adapted to be displaced vertically by thewinding or unwinding of the straps 48.

[0116] When the roller 42 rolls up or folds up the screen 31 (accordingto the embodiment of the invention), it drives around the roller 46which winds up the strap 48, thus raising up the sound broadcastingmeans 60.

[0117] Conversely, on extension of the screen 31, the roller 42 rotatesthe roller 46 in the other direction, which unwinds the straps 48, solowering the sound broadcasting means following a path which issubstantially half that of the weighting bar 33.

[0118] Thus, when the screen that is permeable to sound waves is in theextended position, the sound broadcasting device 60 is located behind itsubstantially at mid-height.

[0119] This is the position that is most favorable to its correctoperation.

[0120] The embodiments given in the present invention are non-limitingexamples of the invention, which is defined by the claims hereinafter.

1. A projection screen of the retractable kind, characterized in that it comprises at least two layers of white fabric transparent to sound waves that are superimposed and joined together.
 2. A projection screen according to the first claim, characterized in that it comprises a weighting bar (23) adapted to tension the two layers of fabric sufficiently to compensate for the differences in length of fabric arising when they are rolled up onto rolling-up means due to the difference in diameter between a layer termed inner layer and a layer termed outer layer which covers it on the said rolling up means.
 3. A projection screen according to the first claim, characterized in that it comprises a combination of lateral hems (34, 35′) containing a plurality of rigid oblong elements (36, 37) adapted to force the folding of the screen into a series of rectangular segments (45), and means for actuating the folding of the screen.
 4. A projection screen according to the preceding claim, characterized in that the said means for actuating the folding of the screen are straps (40) passing through the said hems and passing between the said rigid oblong elements, the said straps being wound onto rolling-up means.
 5. A projection screen according to claim 1, characterized in that it comprises a combination of a band of fabric (51, 51′) disposed according to a path defining hoisting tackle between a rolling-up means comprising at least one fixed roller and at least one mobile roller (55), and means for pressing together two layers of the band of fabric.
 6. A projection screen according to the preceding claim, characterized in that the said pressing means comprise at least two parallel guide means (54, 56) fixed to the said mobile roller (55).
 7. A projection screen according to any one of the preceding claims, characterized in that it comprises means for lowering and raising a sound broadcasting device (60) disposed behind the screen, the said means acting simultaneously with the extension and retraction respectively of the screen. 